MONOCLONAL-ANTIBODY BINDING TO A RECEPTOR ON NONSPECIFIC CYTOTOXIC-CELLS (NCC) INCREASES THE EXPRESSION OF PROTOONCOGENE KINASES AND PROTEIN-KINASE-C

Teleost nonspecific cytotoxic cells (NCC) initiate various cell trigge ring responses following receptor-target cell interactions. A putative receptor protein on NCC may alternatively initiate signalling process es following crosslinkage by homologous anti-receptor mab 5C6. In the present study, we demonstrated that binding to this receptor by mab 5C 6 produced increased levels of expression of cytoplasmic src family pr oto-oncogene kinases lck, fyn and src. The phosphorylated isoforms of each kinase were approximately the same molecular weight (p60). Unlike their mammalian T-cell and natural killer (NK) cell counterparts, NCC p56(lck) did not autophosphorylate on tyrosine residues. This was det ermined by a lack of Western blot reactivity of teleost p56(lck) with anti-phosphotyrosine specific antibodies PT-66 or 4G10. Additional evi dence for this lack of tyrosine phosphorylation was shown by experimen ts treating mab 5C6 activated NCC with sodium orthovanadate. This prot ein tyrosine phosphatase inhibitor did not affect levels of p56(lck) a utophosphorylation. Mab 5C6 activated NCC were also examined to determ ine if levels of protein kinase C (PKC) expression were affected durin g triggering responses. Maximum increased PKC levels occurred 5-10 min following binding. The NCC receptor-activated PKC consisted of a 60,0 00 M(r) isoform and a 30,000 M(r) homologue equivalent to the mammalia n PKC catalytic subunit. Not all kinases examined, however, were affec ted by mab 5C6 binding. Levels of expression of c-myc and cdc2(p34) di d not change following NCC activation. This is the first study of NK-l ike cells in cold-blooded vertebrates regarding the expression of thes e vital intermediary transducing kinases. These enzymes are linked to NCC receptor stimulation and their phosphorylation apparently must pre cede PLC activation and other downstream biochemical events.